Richard Trim: I never said that 4 was. You were wittering on about your odd and even preferences ... I was moving the conversation on to more interesting types of numbers. Just take the primes 37 and 73. Firstly they can be juggled to still be primes and their difference is 36 which is a square number and has an amazing number of factors ie 1 2 3 4 6 9 12 18 ... Shall we carry on .... ha ha